The present invention relates to novel carbazole compounds and to a process for preparing the same, and more particularly to carbazole compounds of formula (I). ##STR6## wherein R represents a C.sub.2.about.4 alkyl group, or a benzyl group; X.sup.1 represents hydrogen, a C.sub.1.about.4 alkyl group, a C.sub.1.about.4 alkoxy group, a halogen atom, a nitro group, an amino group, a C.sub.1.about.4 alkylamino group or a benzylamino group; and n is an integer 1 or 2.
The present invention also relates to a process for preparing carbazole compounds of the formula (II) by allowing phenyl derivatives of formula (III) to react with aldehydes of formula (IV): ##STR7## wherein X.sup.2 represents hydrogen, a C.sub.1.about.4 alkyl group, a C.sub.1.about.4 alkoxy group, a halogen atom or a nitro group; m is an integer 0 or 1; and Y represents a triphenylphosphonium group of the formula ##STR8## wherein Z.sup..crclbar. represents a halogen ion, or Y represents a dialkylphosphonate group of the formula EQU --PO(OR').sub.2
wherein R' represents a C.sub.1.about.4 alkyl group. ##STR9## wherein R represents a C.sub.2.about.4 alkyl group, or a benzyl group.
The thus prepared carbazole compounds according to the present invention are useful as organic photoconductor materials for use in electrophotography, and as fluorescent brightening agents.
Generally, in the art of electrophotography, a photoconductor is electrically charged, for example, by corona charging in the dark, and is then exposed to a light image which selectively dissipates the charges in the illuminated areas of the photoconductor while leaving behind a latent electrostatic image in the non-illuminated areas. This latent electrostatic image may then be developed to form a visible image by depositing finely divided electroscopic marking particles called toner, which toner comprises coloring materials, such as dyestuffs or pigments, on the photoconductor.
Photoconductors for use in electrophotography are required to have the following fundamental characteristics:
(1) The photoconductors must be electrically chargeable to a predetermined potential in the dark. PA1 (2) The photoconductors must retain the electrical charge sufficiently in the dark. In other words, the dark decay of the photoconductors must be small. PA1 (3) The electrical charge on the photoconductors must be dissipated quickly under illumination. In other words, the light decay of the photoconductors must be great and, accordingly, the photosensitivity must be high.
In the production of organic photoconductors, it is required that organic photoconductor materials be dissolvable in solvents conventionally employed in this field, such as aromatic hydrocarbons including toluene and xylene; ketones including methyl ethyl ketone; heterocyclic compounds including dioxane and tetrahydrofuran; and halogenated hydrocarbons including methylene chloride and 1,2-dichloroethane; or mixtures of these solvents.
Furthermore, it is required that organic photoconductor materials be dissolvable in resins, such as polyethylene resin, polypropylene resin, polycarbonate resin, polyester resin and acrylic resin.
Still further, it is required that, when the photoconductor materials are employed as charge transport materials in photoconductors of a double-layered type, comprising a charge transporting layer and a charge generating layer formed on a support material, the charge transporting layer be transparent or nearly so. However, organic photoconductor materials which can meet the just described requirements are not many in number, particularly in the conventional carbazole derivatives.
For example, in Chemische Berichte (Berichte der Deutschen Chemischen Gesellschaft), Vol. 95 (1962), pages 2775 through 2781, there are disclosed 9-methyl-carbazole derivatives. These derivatives, however, are not useful as photoconductor materials, since they cannot be dissolved in the above mentioned resins, and, in the case where those derivatives are dissolved in transparent resins, they tend to be crystallized, making the resin mixture opaque.